Enhancement of α-ketoisovalerate production by relieving the product inhibition of L-amino acid deaminase from Proteus mirabilis

L-Amino acid deaminase(LAAD) is a key enzyme in the deamination of L-valine(L-val) to produce α-ketoisovalerate(KIV). However, the product inhibition of LAAD is a major hindrance to industrial KIV production.In the present study, a combination strategy of modification of flexible loop regions around the product binding site and the avoidance of dramatic change of main-chain dynamics was reported to reduce the product inhibition.The four mutant PM-LAAD^(M4)(PM-LAAD^(S98A/T105A/S106A/L341A)) achieved a 6.2-fold higher catalytic efficiency and an almost 6.7-fold reduction in product inhibition than the wild-type enzyme. Docking experiments suggested that weakened interactions between the product and enzyme, and the flexibility of the "lid" structure relieved LAAD product inhibition. Finally, the whole-cell biocatalyst PM-LAAD^(M4) has been applied to KIV production,the titer and conversion rate of KIV from L-val were 98.5 g·L^-1 and 99.2% at a 3-L scale, respectively. These results demonstrate that the newly engineered catalyst can significantly reduce the product inhibition, that making KIV a prospective product by bioconversion method, and also provide the understanding of the mechanism of the relieved product inhibition of PM-LAAD.

Synthesis and NO production inhibition of novel Mannich base derivatives of irisolidone

Five new C-8 Mannich base derivatives of irisolidone 2a-2e were synthesized and their nitric oxide（NO）production inhibitory activity was evaluated.Compounds 2a,2b,2c and 2e displayed stronger activities in vitro than the parent compound irisolidone.

Hydrolysis of Raw Corn Starch Granules by Glucoamylase and Product Inhibition During the Hydrolysis

Raw corn starch granules were hydrolysized by glucoamylase in a chemostat. The hydro- lysis of three different-sized granules shows that smaller granules undergo more hydrolyzation than larger ones. After 78 h, 9700 of the granules was hydrolysized with diameter between 0.15 mm and 0.3 mm at 50 ℃. When corn starch concentration increased from 100 g/L to 250 g/L, the amount of reducing sugar produced was proportional to the initial substrate concentration and no substrate inhibition phenomenon appeared. In order to study the product inhibition exactly, the product from hydrolysis reaction itself was added into the hydrolysis system at the beginning of starch hydrolysis. Product inhibition with different quantities of product added were studied in the initial several hours, during which period enzyme inactivation could be neglected and product inhibition could be studied separately. The experiments indicate that product inhibition happens when the additional quantity exceeds 9.56 g/L.

Improvement of Concrete Properties and Reinforcing Steel Inhibition Using a Natural Product Admixture

The use of a natural white juice, taken from magrabe banana stem, as concrete admixture to improve mechanical and physicrvchemical properties of concrete has been studied. The compressive strength, bulk density the free lime liberated during hydration and the combined water content were determined. The results indicate that the admixture acts as a retarder in most cases and as accelerator in some ones. Also, the admixture effect on the corrosion resistance of the reinforcing steel against surrounding aggressive media has been investigated using galvanostatic polarization technique. The addition of 0.2% admixture leads to the more inhibition of the steel

Two New Alkaloids from Fusarium tricinctum SYPF 7082,an Endophyte from the Root of Panax notoginseng

Panax notoginseng(Araliaceae)is a famous traditional Chinese medicine mainly cultivated in Yunnan and Guangxi provinces of China.Two new alkaloids,rigidiusculamide E(1)and[-(a-oxyisohexanoyl-N-methyl-leucyl)2-](2),together with two known ones,(-)-oxysporidinone(3)and(-)-4,60-anhydrooxysporidinone(4)were isolated from the mycelia culture of Fusarium tricinctum SYPF 7082,an endophytic fungus obtained from the healthy root of P.notoginseng.Their structures were determined on the basis of extensive spectroscopic analyses.Compounds 1-4 were tested for their inhibitory effects against NO production on Murine macrophage cell line,and the new compound 2 showed significant inhibitory activity on NO production with the IC_(50)value of 18.10±0.16μM.

Anti‑inflammatory and Cytotoxic Triterpenes from the Rot Roots of Panax notoginseng

Four new protopanaxatriol-type triterpenes(1-2)and glucosides(3-4),were isolated from the rot roots of Panax notoginseng(Burk.)Chen,along with four known ones(5-8).Their structures were elucidated on the basis of extensive spectroscopic analysis(HRESIMS,NMR,UV,IR,and OR)and acidic hydrolysis.The possible transformation pathway of these compounds were also speculated from ginsenoside Rg_(1).Compound 1,with a uniqueα,β-unsaturated ketene in its side chain,showed significant inhibitory effects against NO production on Murine macrophage cells(IC_(50)=4.12±0.20μM)and comparable cytotoxicities against five human cancer cell lines(myeloid leukemia HL-60,lung cancer A-549 cells,hepatocellular carcinoma SMMC7721,breast cancer MCF-7,and colon cancer SW480)to positive control,cisplatin(DDP).

Polyhydroxylated eudesmane sesquiterpenoids and sesquiterpenoid glucoside from the flower buds of Tussilago farfara

Chemical fractionation of the n-BuOH partition,which was generated from the EtOH extract of the flower buds of Tussilago farfara,afforded a series of polar constituents including four new sesquiterpenoids(1-4),one new sesquiterpenoid glucoside(5)and one known analogue(6)of the eudesmane type,as well as five known quinic acid derivatives(7-11).Structures of the new compounds were unambiguously characterized by detailed spectroscopic analyses,with their absolute configurations being established by A-ray crystallography,electronic circular dichroism(ECD)calculation and induced ECD experiments.The inhibitory effect of all the isolates against LPS-induced NO production in murine RAW264.7 macrophages was evaluated,with isochlorogenic acid A(7)showing significant inhibitory activity.